My Woods 9000 will operate multiple controls at the same time, do it all the time. Usually two at the same time, boom and dipper. Thats how you scrape a flat botom. If you want to taper up the end of a trench and pack it you need three controls, boom dipper and curl. Also when dumping dirt 2-3 controlls are used at the same time. I kind of make a half circle while dumping. This way your always moving and near the end of the dump your dropping in for the next scoop.
Power seems to be fine using multiple controls just slower.
The trick to not bouncing is finding the balance point on the valve. There is a small area of movement where you hear it hiss a little, thats it.
When first learning I'd have the tractor in 4WD, brakes on hard, bucket down and just take a little weight off the rears. Until your get the feel its easy to drag the tractor all over.
These days it stays in 2wd with the brake off half the time. When ready to move set the heal bucket in the hole. Then reach over and lift the bucket a tad. Lift the stabilzers an inch or so. Then lift the tractor tires up slightly with the boom and push with the dipper. Start out with the dipper straight up an down. You need a gentle touch to do this and a sub frame. Don't think I'd try this with a 3pt set up.
